将 BufWriter 传递给 Rust 中的 function

Question

在此示例中，我试图将BufWriter传递给某些函数，但对泛型类型语法的理解不足以找出缺少的内容。
我不想传递文件，而是想传递缓冲的编写器，但找不到任何可以让我摆脱困境的例子。

use std::fs::OpenOptions;
use std::io::BufWriter;
fn main() {
    println!("Opening dummy read file");
    let write = OpenOptions::new()
        .write(true)
        .create(true)
        .open("DummyWriteFile");
    let mut writer = BufWriter::new(write.unwrap());
    // do some writes with FunctionA
    write_something(&mut writer);

    // write something else here with bufwriter
}

fn write_something(outBuf: BufWriter<W>) {}

我得到的错误如下：

      Compiling playground v0.0.1 (/playground)
error[E0412]: cannot find type `W` in this scope
  --> src/main.rs:13:40
   |
13 | fn write_something( outBuf: BufWriter <W> ){
   |                   -                    ^ not found in this scope
   |                   |
   |                   help: you might be missing a type parameter: `<W>`

For more information about this error, try `rustc --explain E0412`.
error: could not compile `playground` due to previous error

Answer 1

你有几个选择。

要使该版本的代码正常工作，您需要在 function 上添加W作为通用参数，并带有Write绑定。 您需要更改它以获取可变引用：

use std::io::Write;

fn write_something<W: Write>(out_buf: &mut BufWriter<W>) {

}

但是您可能想要的是使用Write特征绑定（因为BufWriter暗示它）而不是直接指定BufWriter ：

fn write_something(mut out_buf: impl Write) {
// OR: fn write_something<W: Write>(mut out_buf: W) {

}